Also see this discussion with related links –
From Tired to Very Fresh - Support - Xert Community Forum (xertonline.com)
Plus @themagicspanner’s version of the chart here –
Adding a Form Colour Chart - Site Feedback - Xert Community Forum (xertonline.com)
Keep in mind the math may not always coincide with how you feel in which case the Freshness Feedback slider comes into play.
Personalizing Xert’s Training Algorithms by using Freshness Feedback – Xert (baronbiosys.com)